The present invention relates to pressurized water reactors of the type comprising a core, formed of prismatic shaped assemblies disposed side by side in a cylindrical core casing having a vertical axis, forming between the core and the casing a space in which a solid partitioning is disposed.
It relates more particularly to reactors of the type in which the solid partioning is formed by a vertical stack of rings surrounding the core, whose external periphery is engaged with a clearance in the casing and whose internal periphery matches the external contour of the core, said rings being centered with respect to the core casing by keys fixed on the casing and projecting into vertical grooves of the rings and being formed with vertical mutually aligned holes defining cooling channels containing plugs leaving restricted flow passages.
In such a reactor, the flow of cooling water is improved as compared to those previously known. In particular, the use of narrow annular flow passages reduces the volume of water in the partioning for a given cooling efficiency and increases the neutron reflecting action.
In the partitioning described for example in French patent No. 87 17923 (or the corresponding U.S. Pat. No. 4,925,624 to Chevereau et al), a pressure balancing chamber is formed between two successive plugs and communicates the annular passages around the plugs. This chamber must have a low height, so as not to represent a significant water volume reducing the reflecting power. Consequently, temperature homogenization does not occur. Now, gamma absorption, and so heat dissipation per unit volume in the partioning, is at a maximum close to the frontier between the partioning and the core and then rapidly decreases in the outward radial direction. Insufficient mixing of the fluid streams in the annular water layer leads to water and partioning heating which is much higher in the zones closest to the frontier.
So that the maximum temperature of the partitioning in these zones remains acceptable, a high cooling flow rate is required. This requires pump oversizing and results in a danger of decreasing the flow rate in the peripheral assemblies of the core.